In current passenger vehicle design, two crash bag modules are typically used. One bag, which inflates to approximately 1 cubic foot in 25 to 35 milliseconds, is mounted in the center of the steering wheel for driver protection and the other bag, which inflates to approximately 10 cubic feet in 60 to 70 milliseconds, is mounted in the right side of the dash for front seat passenger protection.
The methods of inflation currently being used are (1) a compressed gas cylinder augmented by a small charge of solid propellant and (2) a chemical gas generating system utilizing compositions of sodium (or other) azide and an oxidant for generating nitrogen gas. Neither of the foregoing methods has proved to be entirely satisfactory.
The compressed gas devices are necessarily bulky and of complex design. The pressurized cylinder presents hazard problems in shipment, assembly into the vehicle, and vehicle disposal. Because of the difficulty in reliably sealing the pressure cylinder, a pressure monitoring device is normally used in the vehicle to detect gas leakage.
Although the chemical gas generating system obviates the problems associated with the compressed gas system, the use of sodium azide in the chemical system creates other problems. Sodium azide is poisonous when ingested, inhaled as a dust, or absorbed through the skin. In the presence of moisture and an acid environment, sodium azide reacts to form hydrazoic acid, a poisonous gas. Although sodium azide cannot be detonated, contact with many metals, such as copper, lead, and silver may result in the formation of shock- and friction-sensitive explosive azides. In most sodium azide containing gas generating compositions, the solid reaction products contain metallic sodium and sodium oxide, both of which are extremely caustic and reactive. For example, metallic sodium reacts violently with water, liberating flammable hydrogen gas.
The above enumerated properties of azide containing compositions present many problems, particularly in the manufacturing and final disposal processes. Accordingly, it is therefore desirable that a gas generating composition be made available which generates low temperature, non-toxic gases and yields substantially non-corrosive decomposition products.